One known wind turbine is described in PCT Patent Application No. WO 2008/078342 and the embodiments shown in FIGS. 1, 4, 5, 6, 9, 11, 12, 13, 16 and 17, in which the wind turbine comprises at least two electric machines on opposite sides of the supporting structure.
Certain known wind turbines have drawbacks in terms of dependability, because of their complex structural design, and especially the presence of two rotors connected by the transmission. Because the transmission normally has to permit reversible connection, trade-offs are sometimes necessary in terms of rigidity. Moreover, given the dimensions, particularly the axial dimensions, involved, movements caused by rotation, by uneven stress, and by imperfect balancing of the blade assembly are transmitted and amplified by the structure. The dependability and working life of the wind turbine may be affected by severe or prolonged stress (sudden collapse, fatigue failure, etc.).
Some controllable operating quantities affect the stress state of the rotor-transmission assembly. For example, the instantaneous resisting torque necessary to oppose rotation, average rotation speed, and the attack angle of the blades induce different stresses, and could be controlled to attenuate or absorb stress and movements of the rotor-transmission assembly.
Normally available parameters recorded to regulate the wind turbine do not allow for accurately determining the wind turbine's stress state, which means any steps taken to reduce mechanical stress on the rotating parts are substantially ineffective.